Petroleum-based and protein-based adhesives are two general categories of adhesives used in wood composite applications, such as in the manufacture of particleboard, fiberboard, waferboard, oriented strand board (OSB), plywood, and laminated veneer lumber (LVL) from wood particles, fibers, and/or veneers. Both categories of adhesives are known for their ability to polymerize or cure upon heating, thereby bonding wood particles together. Petroleum-based adhesives are known to provide excellent bonding of wood.
In contrast to protein-based adhesives, however, petroleum-based adhesives are not renewable substances that can reduce the dependency on petroleum-based chemicals. Also, petroleum-based adhesives are not biodegradable, so that their use results in an unwanted accumulation of waste. Moreover, stringent regulations on toxic emissions from building materials complicate the use of petroleum-based resins. In particular, most petroleum-based adhesives contain formaldehyde which can contribute to environmental concerns. Despite the relative performance advantages of petroleum-based adhesives, therefore, the art has recognized the potential attractiveness of using protein-based adhesives as alternatives, in order to reduce the usage of petrochemicals and mitigate possible environmental pollution.
For example, protein glues, such as various casein, blood, and soy glue compositions, have been investigated and are discussed in detail, for example, in the Background section of U.S. Pat. No. 6,306,997. The '997 patent itself describes a soybean-based adhesive, containing a cross-linking agent (e.g., a phenol-formaldehyde resin) for preparing wood composite panels.
U.S. Pat. Nos. 6,365,650 and 6,231,985 describe an adhesive suitable for preparing wood composites formed by combining an isocyanate prepolymer with hydrolyzed soy protein at a weight ratio of prepolymer:soy protein in the range of 70:30 to 90:10, i.e., a weight excess of the prepolymer.
U.S. Published Application No. 2002/0153112 A1 describes cellulosic fiber composites (e.g., oriented strand board) having a reduced amount of petrochemicals due to the presence of protein hydrolysates. The composites comprise cellulosic material and a resin binder.
U.S. Pat. No. 5,593,625 describes a particulate material that is formed from a fibrous cellulosic material (e.g., recycled newspaper) and a protein-based resin prepared from a ground leguminous material (e.g., soy flour). The fibrous cellulosic material is combined with the aqueous protein-based resin to form the discrete biocomposite particles. In a preferred embodiment, the particulate material is used to make pressure-formed materials.
U.S. Pat. Nos. 5,344,871 and 5,153,242 describe binders and their use in forming composition board. The binders include high protein agricultural products such as soybean. Binders are taught to be principally protein but cross-linking additives including isocyanates, hindered isocyanates, and diisocyanates may be added.
U.S. Pat. No. 4,282,119 describes an amino resin adhesive, such as a urea-formaldehyde adhesive, with reduced formaldehyde emission by virtue of adding 2-20% by weight of a protein soluble or dispersible in the resin solution. Blood albumin is the preferred protein.
Japanese Patent 81045957 describes adhesives comprising an aqueous solution of animal or vegetable protein (e.g., soy protein) and isocyanate compounds.
Japanese Published Application 4057881 describes compositions containing an isocyanate compound and a water dispersible and/or water soluble polymer (e.g., soluble protein).
Despite the great effort that has been undertaken to develop protein-based adhesives, there remains a need in the art for thermosetting compositions that not only comprise a protein-based component, but also exhibit good bond strength, quick curing properties, and other desirable characteristics traditionally associated with petroleum-based resins. Additionally, such compositions will ideally not contain formaldehyde.
U.S. Published Patent Application US2004/0089418 describes using an adhesive composition for binding wood that comprises a reaction product of (i) a first ingredient selected from a soy protein or lignin and (ii) at least one substantially formaldehyde-free curing agent that includes at least one amine, amide, imine, imide, or nitrogen-containing heterocyclic functional group that can react with at least one functional group of the soy protein, or using an adhesive composition that comprises a reaction product of (i) a protein or lignin, (ii) a first compound that includes at least one amine, amide, imine, imide or nitrogen-containing heterocyclic functional group that can react with at least one functional group of the protein and (iii) a curing agent.